无定型玻璃态聚碳酸酯的塑性行为模拟

用常压分子动力学模拟和固定晶胞能量最小化计算程序,以及构型和能量分析研究了无定型玻璃态聚合物双酚—A—聚碳酸酯(BPA-PC)的塑性变形。计算结果和"势能面理论"架构吻合,此理论将塑性转换解释成"理想结构"之间的相互交叉和塌陷。本方法可以在晶胞尺度有限、高压缩比和低温下对聚合物材料进行模拟,密度、杨氏模量、屈服应变、屈服应力、激化能、激化体积都与BPA-PC的实验数据吻合。     

聚碳酸酯动态黏弹性能与分子取向态的关系

将双酚A型聚碳酸酯(PC)注射成型,基于流动残余应力与分子取向关系的讨论,利用光学双折射法表征样品中的平均分子取向,并考察其动态力学性能.结果表明,近浇口取向大于远浇口,且分子取向态与其动态黏弹性参数间存在关联.当选取损耗角正切值(tanδ)=1的损耗模量值时,发现更高的积分双折射值对应更小的损耗模量,即取向越大动态黏...     

RSM结合GA-BP的聚碳酸酯细长杆轴向变形预测

对聚碳酸酯（PC）注塑的4个工艺变量的GA-BP和RSM 2种优化方法进行了比较,并综合应用2种方法的优点,优化预测了PC细长杆填充过程中的工艺参数。为获得最小的轴向变形,选择模具温度、熔体温度、保压时间、保压压力4个工艺变量,通过RSM获得最优的工艺参数组合为[A3,B3,C1,D1],应用GA-BP预测此工艺条件下的最小的轴向变形值为0.0064 mm, Moldflow软件的模拟值为0.0063 mm,预测精度达到1.58 %;通过与9组随机试验的模拟精度比较,GA-BP和RSM的预测最大绝对误差分别为5.48 %、7.41 %,相对误差分别为2.76 %、3.13 %,通过GA-BP 和 RSM二者联合预测精度有了很大提高。     

注塑工艺对聚碳酸酯制品环境应力开裂行为的影响

研究了不同注塑工艺下成型的聚碳酸酯（PC）平板制品的环境应力开裂行为。结果表明：在四氯化碳浸渍下,在制品侧壁位置出现分层开裂;熔体温度升高可以提升PC制品的耐环境应力开裂性;保压压力较大时,制品开裂现象较为明显。在分析分子取向和残余应力与制品环境应力开裂行为关系的基础上,探讨了注射成型工艺对PC注塑制品环境应力开裂行为的影响机理。     

粹文详摘：CW196热处理对聚碳酸酯环境应力开裂性能的影响

聚碳酸酯(PC)在很多溶剂中容易发生环境应力开裂，它是指塑料在化学介质中受到低于其屈服点的应力或低于其短期强度的应力(包括内外应力及2种应力的组合)的较长期作用发生开裂破坏的现象。环境应力开裂是造成塑料在应用中损坏的主要原因之一，但由于环境应     

聚碳酸酯耐环境应力开裂性能的研究

研究了聚碳酸酯(PC)的耐环境应力开裂(ESCR)行为;探讨了摩尔质量及分布、后处理工艺、温度、溶剂等因素对PC的耐环境应力开裂性能的影响.结果表明:摩尔质量越高,分布越窄,则PC临界应变值越高,耐环境应力开裂性能越好;退火热处理有利于提高PC环境应力开裂性能.此外,温度降低和试样与溶剂溶度参数差Δδ增大均有利于提高PC耐环境应力开裂性能.同时提出了聚合物耐环境应力开裂模型,对环境应力开裂机理进行了探讨.     

模拟生物油分子蒸馏的响应面法工况优化

分子蒸馏是一种高效的生物油分离技术。本文应用刮膜式分子蒸馏装置,对模拟生物油在不同蒸馏温度、蒸馏压力和进料速率下的分离特性进行了研究,考察不同因素对族类化合物蒸出特性的影响。随后采用响应面分析法对模拟生物油分子蒸馏进行了计算机模拟,考察多种因素对分子蒸馏的交叉影响。通过ANOVA分析,模型的F值为21.25,表明模型是显著的。并以目标物酸醛酮在馏分中的质量分数为响应值得到最佳工况：蒸馏温度69.83℃,蒸馏压力1498.31Pa,进料速率5.54mL/min,此时轻质馏分中酸醛酮的质量分数为39.12%。最后在此工况下开展了模拟生物油的验证实验,结果显示馏分中目标物的质量分数为38.96%,与响应面模型吻合良好。模拟生物油经过分子蒸馏后酸醛酮的质量分数由28.50%提升至38.96%,同时酚类的质量分数由37.50%降低到25.14%。     

聚碳酸酯注射成型分子取向分布的双折射实验研究

运用楔块法研究了聚碳酸酯(PC)注塑平板不同位置处厚度方向上的双折射和分子取向分布,同时考察了注射成型工艺和退火处理对制品双折射分布的影响。结果表明,在制品侧壁处出现沿厚度方向上双折射非对称分布的现象;在靠近冷模壁侧,次表层出现双折射峰值或不连续分布;熔体温度和保压压力对厚度方向双折射影响较大;退火处理几乎不影响双折射和分子取向分布。     

新型增韧剂对聚碳酸酯的增韧研究

采用不同种类增韧剂对聚碳酸酯(PC)进行增韧研究,通过冲击试验机、熔体流动速率测定仪、多功能材料试验机和电子分析天平测试了材料的缺口冲击强度、熔体流动速率、拉伸强度、弯曲强度和制品开裂时间。结果表明,随着新型双官能化增韧剂KT-30用量的增加,PC的冲击强度显著提高,材料的熔体流动性和弯曲性能下降较少,而且耐应力开裂性高;KT-30在PC中有很好的分散性,可直接注塑加工;当KT-30用量为5%(质量分数,下同)时,冲击强度约为纯PC的5倍,达到40.8kJ/m2。     

Computer simulation of diffusion within and through membranes using nonequilibrium molecular dynamics

A novel nonequilibrium molecular dynamics (NEMD) method introduced in 1994 and its recent application to investigations of the transport properties of gases and dense fluids within strongly inhomogeneous pore structures are reviewed. In this technique molecular simulations are conducted under realistic nonequilibrium (experimental) conditions thus enabling direct insight into the underlying microscopic processes taking place during transport within pores. The case studies reviewed in this paper establish the versatility and scope of the NEMD technique and also demonstrate its significant advantages over prior molecular simulation procedures as a tool to assist in the design and tailoring of novel nanopore systems.     

Molecular response of a glassy polymer to active deformation

The behavior of a glassy polyethylene-like polymer undergoing active compressive deformation was investigated via molecular dynamics simulation. Several important features can be identified within the stress-strain response of the system. Namely, the system deforms elastically, yields, softens, and then at large strains exhibits strain hardening. Simulations reveal that the actively deforming polymer exhibits several distinct characteristics at the molecular scale. Active deformation is found to significantly increase the transition rate between different dihedral angle states as well as promote the propagation of dihedral angle flips along the chain. When deformation is stopped, the transition rates decrease and propagation of these transitions along the chain is once again hindered. Below the glass transition temperature, transitions are heterogeneously distributed within the system. However, a local density-transition rate correlation study shows that this transitional heterogeneity is not attributable to heterogeneity in the local density. Instead, the high local transition rates must be caused by stresses propagated along the chain backbone as indicated by changes in neighbor correlations with stress. The yield stress is determined as a function of strain rate between strain rates of 10⁸ s⁻¹ and 5×10¹⁰ s⁻¹. The activation volume within the context of the Eyring model is calculated to be 0.21 nm³ for this system.     

Molecular dynamics simulations of deformation mechanisms of amorphous polyethylene

Molecular dynamics simulations were used to study deformation mechanisms during uniaxial tensile deformation of an amorphous polyethylene polymer. The stress-strain behavior comprised elastic, yield, strain softening and strain hardening regions that were qualitatively in agreement with previous simulations and experimental results. The chain lengths, number of chains, strain rate and temperature dependence of the stress-strain behavior was investigated. The energy contributions from the united atom potential were calculated as a function of strain to help elucidate the inherent deformation mechanisms within the elastic, yield, and strain hardening regions. The results of examining the partitioning of energy show that the elastic and yield regions were mainly dominated by interchain non-bonded interactions whereas strain hardening regions were mainly dominated by intra-chain dihedral motion of polyethylene. Additional results show how internal mechanisms associated with bond length, bond angle, dihedral distributions, change of free volume and chain entanglements evolve with increasing deformation.     

Molecular dynamics simulation of small gas molecule permeation through CAU-1 membrane

CAU-1 is one of aluminum-based amine-functionalized Metal–Organic Frameworks(MOFs). Gas permeation and separation behaviors through CAU-1 membrane were simulated by the dual-control plane nonequilibrium molecular dynamics(DCP-NEMD) method. The thickness of membrane was 3.55 nm.Gases CO_2, N_2, CH_4, H_2, He, Kr and Xe were chosen for the calculation in both single component and binary mixtures. The permeation process was calculated in grand canonical(l VT) ensemble with periodic boundary conditions(PBC) in x-and y-directions at different temperatures. The calculated permeance of H_2, CH_4, N_2, CO_2 and Kr decreased with increasing temperature in both single and binary system, while that of Xe with kinetic molecule of 0.41 nm increased with increasing temperature. It shows Xe permeation is governed by activated diffusion. The simulated separation factors of CO_2/N_2 and CO_2/CH_4 of 4.2 and 1.3 respectively were lower than the experimental ones when only considering van der Waals interaction. Further consideration of electrostatic potential leads to improved calculation CO_2/N_2 and CO_2/CH_4 separation factor of 23.0 and 12.9 respectively that were consistent with the experimental ones of 26.2 and 14.8. It suggests the necessity of considering the Coulomb interactions between CO_2 and NH_2-on the pore wall of CAU-1 for permeation of CO_2. For H_2/N_2 and H_2/CH_4 the ideal selectivities also keep consistent with our experimental results. Interestingly, the simulated separation factor for noble Kr/Xe reaches infinite, predicting that CAU-1 membrane possesses potential separation properties for radioactive Kr/Xe.     

Molecular dynamics simulation of water transport through graphene-based nanopores: Flow behavior and structure characteristics

The flowbehavior of pressure-drivenwater infiltration through graphene-based slit nanopores has been studied by molecular simulation. The simulated flow rate is close to the experimental values, which demonstrates the reasonability of simulation results. Water molecules can spontaneously infiltrate into the nanopores, but an external driving force is generally required to pass through the whole pores. The exit of nanopore has a large obstruction on the water effusion. The flow velocity within the graphene nanochannels does not display monotonous dependence upon the porewidth, indicating that the flowis related to the microscopic structures ofwater confined in the nanopores. Extensive structures of confined water are characterized in order to understand the flow behavior. This simulation improves the understanding of graphene-based nanofluidics, which helps in developing a new type of membrane separation technique.     

Growth of tetrahedral amorphous carbon film: Tight-binding molecular dynamics study

Molecular dynamics simulation using tight-binding potential has been performed to examine the growth and performance of tetrahedral amorphous carbon during ion deposition. The sp³ hybrid atom content, density, and compressive stress of the tetrahedral amorphous carbon film depend on the growing conditions such as substrate temperature, ion energy, ion dose, and annealing temperature. The critical temperature for sp³ transition to sp² decreases with ion energy (40, 80, and 120 eV). At low temperatures (<300 K) and low ion energies, the sp³ fraction increases up to 82%. At the annealing temperature less than 1200 K or with a few ions (<20) implanted into the film, its sp³ content and density have only slight changes while the compressive stress has a large reduction with the annealing temperature and the number of implanted ions. This large reduction in the compressive stress is due to a structural relaxation.     

Molecular dynamics simulation of miscibility in several polymer blends

The miscibility in several polymer blend mixtures (polymethylmethacrylate/polystyrene, (1,4-cis) polyisoprene/polystyrene, and polymethylmethacrylate/polyoxyethylene) has been investigated by using Molecular Dynamics simulations performed for fully atomistic representations of short chains. The trajectories obtained from simulation boxes representing the mixtures have been analyzed in terms of the collective scattering structure function. The Flory-Huggins parameter is determined from fits of the simulation results for this function to the random phase approximation expression. The numerical values of this parameter and its variation with temperature obtained with this procedure show a general qualitative and semi-quantitative agreement with existing experimental data for the different systems, though with significant error bars. These results together with those previously obtained for the polyvinylmethylether/polystyrene blends with the same method are compared with data yielded by other computational simpler approaches, which are considerably more sensitive to different parameter choices.     

Molecular dynamics simulation of shear-induced graphitization of amorphous carbon films

The shear-induced graphitization of amorphous carbon (a-C) films in sliding contact with a diamond counterface is investigated by molecular dynamics (MD) simulations. The gradual formation of a graphene-like sp² dominant layer on the a-C film surface is observed after steady-state sliding has been achieved, which provides direct evidence for the experimental observations of friction induced graphitization of a-C film. After the graphitized layer is formed, the relative sliding occurs between the graphitized atomic layers. During the shearing process, the biaxial stress in the graphitized layer experiences a transition from highly compressive (42 GPa) to tensile (−3 GPa). It is the relaxation of the local biaxial stress that leads to the sp³-to-sp² structural transformation.     

Molecular dynamics simulation of PAMAM dendrimer in aqueous solution

The properties of ethylenediamine (EDA) cored and amine surface poly(amidoamine) (PAMAM) dendrimers of generation 1 through 7 in the explicit solvent were studied by the atomistic force field based molecular dynamics. Since amines are assumed to be protonated the simulation condition is designed to represent the dilute alkali solution. All the generations are spherical in shape, while the higher generations show edges or slightly polyhedral shape. The density profile indicates that the dendrimers are constant density spheres and the densities are independent of generation in this aqueous solution. The scaling properties of the radius of gyration with the numbers of atoms and solvent accessible surface with radius of gyration indicate the PAMAM dendrimers are densely compact structures which result from the highly flexibility confirmed by the terminal group distribution. Dynamic behaviors such as autocorrelation function of the squared radius of gyration and mean square displacement were also studied too.